Motivated by recent core-level x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) experiments for the newly-discovered superconducting infinite-layer nickelate, we investigate the core-level spectra of the parent compounds NdNiO2 and LaNiO2 using the combination of local density approximation and dynamical mean-field theory (LDA+DMFT). Adjusting a charge-transfer energy to match the experimental spectra, we determine the optimal model parameters and discuss the nature of the NdNiO2 ground state. We find that self-doping from the Nd 5d states in the vicinity of the Fermi energy prohibits opening of Mott-Hubbard gap in NdNiO2. The present Ni L3 XAS and RIXS calculation for LaNiO2 cannot explain the difference to NdNiO2 spectra.

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Motivated by recent hard x-ray photoemission spectroscopy (XPS) experiment for trivalent Fe oxides Sr2FeMoO6 (ferrimagnetic correlated metal) and LaFeO3 (antiferromagnetic Mott insulator) (Phuyal et al 2021 J. Phys. Chem. C 125 11249–56), we present a theoretical analysis of the Fe 2p core-level spectra using a computational method based on local density approximation combined with dynamical mean-field theory. We find that a nonlocal screening (NLS) effect in the XPS final states is crucial for interpreting the experimental XPS result of both the Fe oxides. A close relationship between the NLS feature in core-level spectra and a long-range magnetic ordering is emphasized.

We have investigated the local Fe electronic changes in the square planar Fe(II) compound SrFeO2 by x-ray emission (XES) and x-ray absorption spectroscopy (XAS) through the pressure-induced spin transition up to 60 GPa. The analysis of Fe Kβ XES confirms the transition under pressure from a high spin to intermediate spin state at Pc = 43 GPa while XAS at the Fe K-edge reveals the spectral signatures of the lattice compression under pressure. Simulations of the XAS spectra point to significant changes in Fe p-d states across Pc through the hybridization with the O p states eventually leading to the magnetic instability.

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